At the present time, various types of displays are used, and the practical use of various types of displays is studied. All of these displays except for cathode-ray tube types aim at a reduction in thickness. Further, there is an increasing demand for flexible types. Displays are installed for a long period of time and, in use, are exposed to severe environment conditions and, for example, undergo the influence of electric potential and temperature rise. Further, materials involved in luminescence or light modulation of displays cannot be said to have high chemical stability.
For example, for color displays using organic EL elements, when color display is provided using a luminous body, in general, three primary colors of blue, green, and red are obtained by changing the luminescent color of the luminescent body per se, or by using color filter layers and/or fluorescence conversion layers formed of fluorescent materials. Patterning (referred to as pixels) of EL elements of the three primary colors results in lowered efficiency of elements or suffers from a very complicated process, and, thus, mass production is difficult, and, at the same time, the cost is high.
For a dye- or pigment-colored resin film in the color filter layer and/or the fluorescence conversion layer, the presence of a small amount of moisture and /or organic component, which exists outside the element or stays or is contained in the element, adversely affects a luminescent element in a color display and is causative of lowered luminescence life and the occurrence of dark spots. Further, since the color filter layer and/or the color conversion layer are formed by patterning, a level difference among three primary color layers and minute projections at the edge of the patterns and the like exist, and concaves and convexes are present over the whole surface of the resin film. This poses a problem that defects and breaking occur in the electrode film and, consequently, the function as the display element cannot be provided.
What is required of the filter substrate used in the color display and the color conversion-type color display is that the filter substrate does not permit a significant level of permeation of moisture and/or organic component, possesses excellent environment resistance, does not adversely affect the luminescent element in a display, causes no significant level of lowering in luminescence life, and occurrence and growth of dark spots, is less likely to cause breaking of the electrode, is highly reliable, and, at the same time, can be easily produced and is low in cost.
It is known that a protective layer (an overcoat layer in the present invention) is provided in display elements from the viewpoint of shielding a fluorescent substance layer against moisture and the like (see, for example, Japanese Patent Laid-Open No. 219786/1999). In this case, however, an isocyanate-cured urethane resin, which is different from a material for a protective layer in the present invention (an overcoat layer in the present invention), is used as the protective layer.
Further, it is known that a protective layer (an overcoat layer in the present invention) is provided from the viewpoint of shielding a fluorescent substance layer against moisture and the like (see, for example, Japanese Patent Laid-Open No. 260562/1999). In this case, however, a heat- or ultraviolet-curing resin such as an acrylic resin, which is different from a material for a protective layer in the present invention (an overcoat layer in the present invention), is used as the protective layer.
Furthermore, it is known that a barrier layer is provided for shielding a fluorescent substance layer against moisture and the like. Examples of this technique known in the art include a method in which the thickness of the barrier layer is limited (see, for example, Japanese Patent Laid-Open No. 117976/2002) and a method in which oxynitride silicon having a limited composition is used in the barrier layer (see, for example, Japanese Patent Laid-Open No. 39468/2004). These publications, however, neither describe nor suggest materials for the protective layer.
Further, regarding materials for layers, materials equivalent to the material for the protective layer in the present invention are known (see, for example, Japanese Patent Laid-Open No. 295848/1996). However, the function of these materials contemplated in this publication is gas barrier properties, and this publication neither describes nor suggests the use of these materials for flattening.